diff --git a/dd-java-agent/instrumentation/grpc-1.5/src/main/java/datadog/trace/instrumentation/grpc/server/MethodHandlersInstrumentation.java b/dd-java-agent/instrumentation/grpc-1.5/src/main/java/datadog/trace/instrumentation/grpc/server/MethodHandlersInstrumentation.java
index 35cc6e901ba..14c08edc9ed 100644
--- a/dd-java-agent/instrumentation/grpc-1.5/src/main/java/datadog/trace/instrumentation/grpc/server/MethodHandlersInstrumentation.java
+++ b/dd-java-agent/instrumentation/grpc-1.5/src/main/java/datadog/trace/instrumentation/grpc/server/MethodHandlersInstrumentation.java
@@ -59,7 +59,7 @@ public static void onEnter(@Advice.Argument(0) Object serviceImpl) {
         if (superClass != null) {
           // bindService() would be the only method in this case and it's irrelevant
           if (superClass.getDeclaredMethods().length == 1) {
-            for (Class<?> i : serviceClass.getInterfaces()) {
+            for (Class<?> i : superClass.getInterfaces()) {
               if (i.getSimpleName().equals("AsyncService")) {
                 superClass = i;
                 break;